JulianDate (SSS Util)

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edu.nrao.sss.measure
Class JulianDate

java.lang.Object
  edu.nrao.sss.measure.JulianDate

All Implemented Interfaces:: Cloneable, Comparable<JulianDate>

public class JulianDate
extends Object
implements Cloneable, Comparable<JulianDate>
extends Object
implements Cloneable, Comparable<JulianDate>

A Julian Date.

Wikipedia's definition:

The Julian day or Julian day number (JDN) is the integer number of days that have elapsed since the initial epoch defined as noon Universal Time (UT) Monday, January 1, 4713 BC in the proleptic Julian calendar...The Julian date (JD) is a continuous count of days and fractions elapsed since the same initial epoch.

As is the case with the Date class, this class models a date/time concept, not a pure date.

Note on the use of the Gregorian Calendar
This class uses java's GregorianCalendar class to handle historical oddities in day tracking. That class sets the year for the switch over from the Julian to the Gregorian calendar as 1582; England and its colonies, including America, did not convert until 1752. That class also uses the Julian calendar for dates prior to the change to the Gregorian, and then a proleptic Julian for dates prior to 1 March 4 AD. What this means for us is that the conversion of a Julian Date to the more familiar form may not produce the expected results for dates prior to 1753. Since our main use for this class is for more recent dates, and since this class is backed by java's standard calendar, we should not be overly concerned with conversion of dates in the distant past.

Note on Precision
The java Date class has a resolution of one millisecond (1ms). This class employs techniques to keep the resolution of this class as close to that of Date as possible. The goal is to make code like this work without complaint.

   Date       origDate  = someFuncThatReturnsDate();
   JulianDate jd1       = new JulianDate(origDate);
   JulianDate jd2       = new JulianDate(jd1.value());
   Date       otherDate = jd2.toDate();
   
   if (!origDate.equals(otherDate))
     complainVigorously();

Without taking pains in the class to make certain the above works properly, the two times could have been off by a millisecond.

Version Info:

$Revision: 1578 $

$Date: 2008-09-24 13:34:32 -0600 (Wed, 24 Sep 2008) $

$Author: dharland $ (last person to modify)

Since:: 2007-08-01
Author:: David M. Harland

Constructor Summary
`JulianDate()` Creates a new instance for the current time.
`JulianDate(BigDecimal julianDate)` Creates a new instance for the given Julian Date.
`JulianDate(Date gregorianCalendarDate)` Creates a new instance for the given Gregorian calendar date.
`JulianDate(int julianDayNumber)` Creates a new instance for the given Julian Day Number.
`JulianDate(String julianDate)` Creates a new instance for the given Julian Date.

Method Summary
`JulianDate`	`add(BigDecimal days)` Increments this date by the whole and fractional `days`.
`JulianDate`	`add(TimeDuration duration)` Increments this date by the given amount of time.
`JulianDate`	`clone()` Returns a copy of this date.
`int`	`compareTo(JulianDate otherDate)`
`int`	`dayNumber()` Returns the Julian Day Number for this date.
`boolean`	`equals(Object o)` Returns true if `o` is equal to this Julian date.
`BigDecimal`	`fraction()` Returns the fractional portion of the value of this date.
`int`	`hashCode()` Returns a hash code value for this Julian date.
`boolean`	`isAfter(JulianDate other)` Returns true if this date is later than `other`.
`boolean`	`isBefore(JulianDate other)` Returns true if this date is earlier than `other`.
`static JulianDate`	`makeFromMjd(BigDecimal modifiedJulianDate)` Returns a new `JulianDate` for the given MJD.
`static JulianDate`	`makeFromMjd(String modifiedJulianDate)` Returns a new `JulianDate` for the given MJD.
`static JulianDate`	`makeMjdZero()` Returns a new `JulianDate` whose time is set to the instance that MJD equals zero.
`int`	`modifiedDayNumber()` Returns the Modified Julian Day Number for this date.
`BigDecimal`	`modifiedFraction()` Returns the fractional portion of the modified value of this date.
`BigDecimal`	`modifiedValue()` Returns the real number representation of the Modified Julian Date (MJD) corresponding this date.
`JulianDate`	`set()` Sets this date to the current time.
`JulianDate`	`set(BigDecimal julianDate)` Sets this date to the given time.
`JulianDate`	`set(Date gregorianCalendarDate)` Sets this date to the given time.
`JulianDate`	`set(int julianDayNumber)` Sets this date to the given time.
`JulianDate`	`set(String julianDate)` Sets this date to the given time.
`JulianDate`	`setFromMjd(BigDecimal modifiedJulianDate)` Sets this date to the given time.
`JulianDate`	`setFromMjd(String modifiedJulianDate)` Sets this date to the given time.
`JulianDate`	`subtract(BigDecimal days)` Decrements this date by the whole and fractional `days`.
`JulianDate`	`subtract(TimeDuration duration)` Decrements this date by the given amount of time.
`Date`	`toDate()` Returns a date in the Gregorian, Julian, or proleptic Julian calendar corresponding to this date.
`BigDecimal`	`toEpoch()` Returns the Julian Epoch for this date.
`String`	`toString()`
`String`	`toString(int minFracDigits, int maxFracDigits)` Returns a text representation of this Julian Date.
`TimeOfDay`	`toTimeOfDay(TimeZone timeZone)` Returns the time of day, in the given time zone, for this Julian Date.
`TimeOfDay`	`toTimeOfDayLocal()` Returns the time of day, in the local time zone, for this Julian Date.
`TimeOfDay`	`toTimeOfDayUtc()` Returns the UTC time of day for this Julian Date.
`BigDecimal`	`value()` Returns a real number representation of this date.

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Constructor Detail

JulianDate

public JulianDate()

Creates a new instance for the current time. See the class comments for an explanation of the use of the Date class.

JulianDate

public JulianDate(Date gregorianCalendarDate)

Creates a new instance for the given Gregorian calendar date. See the class comments for an explanation of the use of the Date class.

JulianDate

public JulianDate(BigDecimal julianDate)

Creates a new instance for the given Julian Date.

The actual value used by this object may differ from the parameter value by as much as 10^-7. This is because this class attempts to mimic the millisecond resolution of java's Date class. See the class comments for a longer explanation.

JulianDate

public JulianDate(String julianDate)

Creates a new instance for the given Julian Date.

Since:: 2008-08-14

JulianDate

public JulianDate(int julianDayNumber)

Creates a new instance for the given Julian Day Number.

Method Detail

makeMjdZero

public static JulianDate makeMjdZero()

Returns a new JulianDate whose time is set to the instance that MJD equals zero.

Returns:: a JulianDate where the modifiedValue() is zero.
Since:: 2008-09-23

makeFromMjd

public static JulianDate makeFromMjd(BigDecimal modifiedJulianDate)

Returns a new JulianDate for the given MJD.

Parameters:: modifiedJulianDate - the intial MJD for this Julian Date.
Returns:: a new JulianDate for the given MJD.
Since:: 2008-09-23

makeFromMjd

public static JulianDate makeFromMjd(String modifiedJulianDate)

Returns a new JulianDate for the given MJD.

Parameters:: modifiedJulianDate - the intial MJD for this Julian Date.
Returns:: a new JulianDate for the given MJD.
Since:: 2008-09-23

set

public JulianDate set()

Sets this date to the current time. See the class comments for an explanation of the use of the Date class.

set

public JulianDate set(Date gregorianCalendarDate)

Sets this date to the given time. See the class comments for an explanation of the use of the Date class.

Parameters:: gregorianCalendarDate - the common form of a date.
Returns:: this date.